[OSM-dev] Consensus on areas?

[Etienne]

On 9/1/06, Lars Aronsson <lars at aronsson.se> wrote:
>
> On August 28, Etienne wrote:
>
> > A way *is* an ordered list of nodes (sort of).  A way is defined
> > as an ordered list of segments.
>
> That's not how ways are currently used on OSM.  I frequently draw
> two parallel sequences of line segments for a motorway, and then
> add all segments to one way, like this:
>
>   o---A---o---B---o---C---o---D---o
>
>   o---E---o---F---o---G---o---H---o
>
>   way: name=E4 ; class = motorway ;
>        segments = ( A, E, B, F, C, G, D, H )
>
> Then when I discover there is an off-ramp connecting at the middle
> of segment G, I remove that line segment, create a new node and
> two new line segments, then I add these segments to the way:
>
>
>   o---E---o---F---o-K-o-L--o---H---o
>                        \
>                         M--o
>
>        segments = ( A, E, B, F, C, D, H , K , L )
>
> Why?  Because what I want is a means to name the road and classify
> it as a motorway.  I don't need the sequence, only the grouping.


For naming and classification purposes the sequence is not important.  But
it is very important for route planning software, which needs to know where
a road starts and where it ends.  The sequence is also important for
software that wants to render street names along the path of the way.

You are not going to get very good results if you tag roads like this and it
is not the way that most people are tagging things in OSM, at least in all
the examples I've seen.

If the sequence of line segments are grouped on a lower level,
> which is something I support, I still need a means on top of that
> to group, name and classify the parts that make up a road.  The
> sequence of segments cannot fully replace the ways we have today.


Hierarchical grouping of ways seems to be generally accepted now as a
necessary feature.  If they get implemented then segments will no longer be
required.  All existing segments would need to be recreated as two node
ways.  This will be a very big step forward.

--
>   Lars Aronsson (lars at aronsson.se)
>   Aronsson Datateknik - http://aronsson.se
>
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